What's the intended use of the PC ? Really need/want 32GBs RAM ? If yes...best to get it upfront otherwise it may be hard to match as time goes on.
Re QVL.....there's lots of places to look but doubt you'll find a lot of the newest RAM (using the 8GB modules) listed for an older MBs like the ASUS P8Z68-V Pro/Gen3. Places I'd look....RAM resellers like Crucial, Corsair, Mushkin, etc; the ASUS forums for users with that same MB, Newegg.com for buyer remarks on those who bought that ASUS MB and who specify their system components, etc., etc., etc.,
Here's one link but note the pricing.....the higher-speed, lower-wait state RAM in the 8GB modules is expensive as you should expect.
BTW ....why use slower RAM running as CAS 10 ? Aren't you looking to make it run fast ?